The present invention generally relates to the construction of a linear-type actuator for generating driving force with the use of elastic vibrations to be obtained by the piezo-electric effect of a piezo member, and a method of driving it.
In recent years, a linear-type actuator is watched, where elastic vibrations are excited upon the vibrator consisting of a piezo member such as piezo ceramic or the like so as to use them as driving force.
The conventional linear type actuator will be described hereinafter in conjunction with the one shown in FIG. 1.
FIG. 1 is a schematic view of the conventional linear-type actuator shown in Japanese Patent Laid-Open Publication No. 63-283473. Referring now to FIG. 1, there provides integrally a driver member 2 on the one surface of a basic member 3, and a vibrator 1 is composed of piezo elements 4a, 4b, 4c being stuck, as shown in FIG. 2, on three faces except for driving the vibrator 1 on the basic member 3 with the driver member 2 being integrally projected.
The vibrator 1 constructed as mentioned above is excited in the diagonal line E - F or G - H direction of the vibrator 1 of FIG. 1 so that a slider (not shown) which has been brought into pressure contact onto the driving member 2 can be driven. A voltage V.sub.1 to be expressed by the (1) equation is applied upon the piezo element 4a, a voltage V.sub.2 expressed by the (2) equation is applied upon the piezo elements 4b, 4c. EQU V.sub.1 =V.sub.0 X sin (.omega.t) (1) EQU V.sub.2 =V.sub.0 X cos (.omega.t) (2)
where V.sub.0 is an instantaneous value of a voltage, .omega. is a angular frequency, t is time.
Bending vibrations for effecting elliptic movement expressed by the (3) equation are excited upon the driving member 2 of the vibrator 1 at the top end of the driving member 2. EQU .xi.=.xi..sub..theta. X (cos (.omega.t)+sin (.omega.t)) (3)
where .xi. is an amplification value of bending vibrations, .xi..sub.0 is an instantaneous value of bending vibrations.
A slider established in pressure contact against the end of the driving member 2 of the vibrator 1 by the movement of the elliptic track by frictional force is driven in the movement direction of the elliptic track by the frictional force. Also, the movement can be effected in a direction opposite to the above description by the change in phase.
In the construction of the conventional linear- type actuator, the bending rigidity of the vibrator in the Y direction to be driven by the piezo member becomes large with providing the driving member 2 to be different from the bending rigidity of the vibrator in the X direction, and the resonance frequency and impedance of the piezo element 4a taken from the side of driving element become largely different from the resonance frequencies and impedances of the piezo members 4b and 4c.
Therefore, even if the voltages v1 and v2 expressing with the equations (1) and (2) are loaded on, the vibration amplitudes in the X and Y directions are different from each other to lower largely the driving efficiency of slider. The driving circuit, the controlling circuit and so on become complicated if the vibration amplitude in the X, Y directions is made to be set in approximately the same extent. As the change in the bonding rigidity by the driving member 2 causes the slip in the node position of the displacement distribution in the X, Y directions due to not specifying the position for supporting the driver member, the vibration loss by the support fixing operation of the vibrator becomes larger so as to reduce the driving efficiency.
Although the moving direction of the slider is changed with the composite resonance by the piezo member provided on an orthogonal plane and the phase of the vibration in the X, Y directions, the efficiency is not expected to be improved, because approximately double inputs are required because of the change in the moving direction. That's why the vibration displacement amount is not increased by the composition of two vibrations.
The driving member and the slider come into contact against each other on the plane, with a problem of lowering the driving efficiency and causing the noises when the plane accuracy is inferior. Further, when the plane accuracy is improved, there is a problem in that the mass production and manufacturing cost increase are caused.